Production of primary alkylation products in hf alkylation



Patented Apr. 19, 1949 PRODUCTION OF PRIMARY ALKYLATION PRODUCTS IN HF ALKYLATION Jack Calhoon Dart, Carl S. Kuhn, Jr., and Joe E. Penick, Dallas, Tern, and Urban H. Wagner, Woodbury, N. J., assignors, by mesne assignments, to Soccny-Vacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application November 29, 1944, Serial No. 565,794

1 Claim.

This invention relates to the production of high octane motor fuel and relates more particularly to the production of high octane motor fuel by the catalytic alkylation of isobutane with butenes.

As is well known, high octane motor fuel can be produced by the alkylation of low boiling isoparaffins with low boiling olefins in the pres ence of suitable catalysts, whereby the isoparaffins condense with the olefins to form saturated compounds within the gasoline boiling range. While various isopararfins and olefins may be employed for this alkylation reaction, those containing four carbon atoms to the molecule are especially desirable not only because they produce alkylate products having highly desirable octane ratings and volatility characteristics but also because they are readily available in large quantities. Commonly, charge stocks for the production of alkylate motor fuel comprise butanebutene mixtures obtained, for example, by dehydrogenation of butane fractions separated from natural gas or straight run naphthas, fractionation of cracking still gases, etc, and these charge stocks contain all the butane and butane isomers, namely, isobutane, normal butane, isobutene, butene1, and butene-2 in varying although significant proportions. A particularly satisfactory alkylation catalyst is hydrofluoric acid and the present invention is concerned with the alkylation of isobutane with butene mixtures employing hydrofluoric acid as the effective catalytic agent.

It is an object of this invention to provide a new and improved process for producing motor fuels by the hydrofluoric acid alkylation of isobutane with the various isomeric butenes. It is another object of this invention to improve the yield of motor fuel obtained by the hydrofluoric acid alkylation of isobutane with butene mixtures. It is a further object of the invention to provide a process for the production of motor fuel having an increased octane rating the hydrofluoric acid alkylation of isobutane with butene mixture. It is another object of the invention to improve the yield of aviation motor fuel obtained by the hydrofluoric acid alkylation of isobutane with butene mixtures. urther objects of the invention will be apparent from the following description.

Inaccordance with our invention, high octane motor fuel is produced from a butane-butane mixture by a process which involves a correlation of the factors of residence time of the hydro carbon reactants and reaction products in contact with the catalyst with the reaction temperature and with the relative proportions of the isomeric; butenes in the feed stock.

We have discovered that an increase in the octane rating and yields (on the basis of butenes consumed) of motor fuels produced by the hydro-- fluoric acid alkylation of butane-butene mixtures is obtained by a proper correlation of the factors of residence time, temperature. and composition of the feed stock relative to the varying proportions of isomeric butene therein for otherwise con. stant conditions of external isoparafiineolefin ratio, titratable acidity of catalyst, acid-hydro carbon ratio, degree of contacting, etc.

In the alkylation reaction it has been considered that factors such as isobutane-olefin, ratio, temperature and concentration of the hydrofluoric acid catalyst, expressed as titratable acidity, were the principal factors. Time of con.- tact has been referred to, but not considered an important variable, and residence times (defined hereinafter) of reactants in contact with catalysts-have been suggested of from as little as.

one minute to as much as several hours, with present commerical butane-butene alkylation utilizing residence times of from 15 to 40 minutes. Recently two of us have discovered that the nature of the butene isomer subjected to the alkylation reaction affects the yield andquality of the product, isobutene and butene-2 giving alkylate products in superior yield and quality to butene-l, as disclosed and claimed in our copending application, Serial No. 532,749, filed April 26, 1944. Another variable capable of aifecting the nature of the reaction is the ratio of acid catalyst to hydrocarbons, which should preferably be high as disclosed and claimed in the copending application of Urban H. Wagner, Joe E. Penick and Carl S. Kuhn, Jr., Serial No. 561,888, filed November 4, 1944, and now abandoned. Additionally, the manner of contacting the reactants with the catalyst afiects the yield and quality of the product, i. e., as disclosed and claimed in the copending application of Joe E. Penick, Serial No. 561,889, filed November 4,

1944, and now patent No. 2,431,500, the olefin should preferably be contacted with the catalyst in such a manner that the maximum olefin content occurs in the reaction mixture at a point wherein the ratio of isobutane to higher isoparaflinic hydrocarbons is a maximum to minimize secondary alkylation reactions between primary alkylate products and olefins. As disclosed in the said Penick application this may advantageously 4 be'effected by flowing a mixture of other isoparafi'in, olefin and catalyst in a single pass through an elongated reactor with recirculation of catalyst only from the reactor effluent.

In spite of intensive experimentation with the many variables possible in HF alkylation, many inconsistencies in results were obtained espec ally where more than one variable in reaction conditions was altered at an one time. We have now discovered that the factors of time, temperature and nature of the isomeric butenes charged are interrelated in their effect upon the yield and quality of the alkylate product.

Alkylation is a complex reaction apparently involving first the formation of primary alkylate products at the expense of the consumption of isoparaffin and olefin in approximately equimolar proportions. This reaction is quite rapid, the actual time required depending very largely upon temperature, but of course subject to a lesser extent to such variables as titratable acidity of the HF catalyst, isoparafiin-olefin ratio, concentration of the olefin in the reaction mixture, degree of contacting, etc. The exact time required for this reaction has not been ascertained because of the rapid nature of the reaction and the diificulty of separating reactants from catalyst to stop further reaction within times necessary to study this factor with accuracy. We have demonstrated, however, that the reaction at 20 C. is complete in so far as the initial alkylation is concerned in less than three seconds. At lower temperatures the reaction time required is increased and at higher temperatures the initial reaction may require but a fraction of a second with good contacting. These time requirements are generally true to the extent that they are subject to determination with the ordinary variables of catalyst concentration, proportions of reactants, methods of contacting, etc., employed.

Following the completion of the initial alkylation reaction other reactions involving the primary alkylate product and catalyzed by the hydrofiuoric acid occur. These reactions in summation involve isomerization and disproportionation of the primary alkylate product. With butane-butene alkylation the primary product, regardless of whether the reaction is one of direct union of a molecule of isoparafiin and olefin or one of polymerization of the olefin followed by hydrogen exchange between the polymer and the isoparafl'in reactant, is a branched chain octane. This primary octane product or the primary octane products, where more than one primary product may be obtained, undergo isomerization towards the equilibrium isomeric mixture at the reaction temperature employed. Disproportionation of the octanes to lower boiling heptanes, hexanes and pentanes and higher boiling nonanes, decanes, etc., will also occur. The extent to which these reactions occur will again depend upon the reaction time, and the temperature at which these various reactions are carried out, a factor that is determinative of the reaction rates for these isomerization and disproportionation reaction. The reaction mechanics of these isomerization and disproportionation reactions may be the same, i. e., dealkylation of the octanes into isoparafiin and olefin in various combinations followed by alkylation of the dealkylated material in accordance with the theory advanced in the copending application of Carl S. Kuhn, Jr., Serial No. 455,775, filed August 22, 1942, now U. S. Patent 2,i03,929.

-Regardless of the mechanism of the reaction there is a definite tendency of the primary alkylate product to undergo isomerization and disproportionation to an alkylate product containing significant proportions of hydrocarbons of from 5 to 10 or more carbon atoms and containing many of the possible isomeric pentanes, hexanes, heptanes, octanes, nonanes, decanes, etc.

Whatever may be the nature of these various isomerization and disproportionation reactions, they all have their own reaction rates dependent upon temperature primarily as well as the other reaction conditions to a lesser extent. The disproportionation to higher and lower boiling hydrocarbons, however, is also influenced to a considerable extent by the relative amount of ex cess isobutane in the alkylation reaction mixture, being less the greater the amount of isobutane present. Here also, though primarily because of the complex nature of these isomerization and disproportionation reactions, the actual reaction rates and the time required for the various reactions to go to completion at various temperature levels and reaction conditions have not been determined. These latter reactions are, however, relatively slow compared to the alkylation reaction. although since they being as soon as the alkylate is formed some secondary alkylation products are necessarily formed.

The products particularly desired in isobutanebutene alkylation are the various trimethyl pentanes because of the Very favorable octane ratings of these hydrocarbons. With some of the isomeric butenes these highly desirable trimethyl pentanes represent the principal primary products of the reaction and any secondary alkylation reactions of isomerization or disproportionation which tend to result in a decrease in the proportion of the trimethyl pentane products is undesirable. Isobutene is an example of such a butene and in the alkylation of this olefin with isobutane it is desirable to stop the reaction by stopping furt er contact between the alkylate product and the effective catalyst as soon as the initial alkylate product is formed. Similarly, butene-2, when alkylated with isobutane in the presence of hydrofluoric acid, gives primary alkylate products high in the desirable trimethyl pentanes. The trimethyl pentanes are caused to isomerize to less desirable octanes or disproportionate to less desirable heptanes, nonanes, etc., by further contacting with the cat alyst and here also the quality is adversely affected by further contacting of alkylate product with catalyst.

On the other hand, in the case of butene-1, the primary alkylate products are of poor quality containing considerable quantities of dimethyl hexanes and further contacting of catalyst with the alkylate products is highly desirable since isomerization results in the formation of products of improved quality. Since there is a third reaction involved, disproportionation, and excessive disproportionation of a butene alkylate is generally not desirable, the amount of the further contacting of the butene-l alkylate should be limited to that beyond which the rate of octane improvement due to isomerization of the Ca hydrocarbons becomes relatively slow because of approach to equilibrium concentrations. Further contacting achieves relatively little isomerization of the Ca hydrocarbons and merely results in increased breaking-up of the Ca hydrocarbons to higher and lower hydrocarbons of generally lower octane rating, and a loss in yield of aviation blending material. Here again the exact time is diflicult; to fix primarily because of the eflectof excess isobutane in slowing down this disproportionation reaction and the amount of this excessisobutane utilized may vary widely, and also. because of the eifect of such factors as temperature upon the isomerization equilibrium values and rates of the reactions involved.

In other. words, with two of the three butene isomers theso-called secondary alkylation reactions adversely affect product quality while with the third a controlled amount of further contacting is beneficial to product quality.

The contact times at a given temperature for the alkylation reaction to go to completion while subject to some variations are of apparently substantially the same order of magnitude for practical considerations for all three butene isomers. The rates of the secondary alkyl-ation reactions appear to vary somewhatmore widely, particularly the rates for formation of the undesirable decomposition products from isobutene and butene- 2 alkylate are apparently more rapid than the rates for the desirable secondary reactions occurring in butene-l alkylate, or at least the time required for a given loss in product quality as determined by octane rating change is less in the case of butane-2 or isobutene alkylate, than the time required for a corresponding increase in octane rating in. butene-l alkylate.

From the foregoing it is now apparent that the actual preferred residence time may be very short in the case of butane-butene stocks containing little or no buteneand may be relatively high where such stocks contain relatively large amounts of butene-l as compared with the other butene isomers. The actual time to be employed will of course depend upon temperature and to a lesser extent upon the other factors previously mentioned as influencing the alkylation reaction. The optimum product from the standpoint of octane rating for given reaction conditions will be obtained by eliminating the butene-l more or less completely from the butane-butene feed stock and by carrying out the reaction under such conditions that product and catalyst are separated as rapidly as possibleafter the desired reaction has been completed. Because of the large number of additional variable effecting the reaction absolute values for the most desirable contact time at any given temperature cannot be definitely given. We have found, however, that at C. when utilizing a butane-butene mixture in which not more than volume percent of the total olefinic constituents is butene-l, that contact times for liquid phase alkylation of as low as about 3 seconds give satisfactory yields and that contact times of from 2.1 to 42 seconds result in optimum product quality with the best quality obtained at the lower values of time within the range indicated and high yields of the desired products so long as good contacting of reactants and catalyst are maintained.

The alkylation process according to our invention may be conducted in any way known to the art so long as the conditions of time, temperature and isomeric butene distribution are properly correlated.

Usual commercial practice involves the contacting of an agitated emulsion of isobutane, hydrofluoric acid, alkylate product and olefin in a reactor from which a portion of the emulsion is continuously withdrawn and into which fresh acid (including recycle acid), fresh isobutane (including recycle isobutane), and olefin are continuously introduced. Acid-hydrocarbon ratios of about 1 to 1, and isobutane-olefinratiosof 2 to 1 to l5,to 1 are utilized in the feed. The withdrawn emulsion is then allowed to settle by gravity into an acid phase for recycle, and a hydrocarbon; phase from which product alkylate and recycle isobutane are recovered. Residence times, de-- fined as the total volume of hydrocarbons in the reaction zone'divided by the total rate of hydrocarbon feed per minute, of from 15 to 40 minutes are usually used at temperatures from 60- to 120. F. Additionally, since some time is required for separation of the acid and hydrocarbon phases in the emulsion in the settling zone, a further time of contact is involved. This time of contact is short and negligible on the average relative to the residence times usually employed being from 30 seconds to about 2 minutes for complete separation dependin upon the design of the settling tank, but it becomes an appreciable factor where extremely short (as compared with the present commercial practice) residence times are employed. Mathematically it is capable of calculation by noting the time rate of resolution of the emulsion and an average contact time for separation may be determined.

The present invention contemplates the control of the total average actual contact time of hydrocarbon reactants and acid catalyst, including residence time in the usual sense and the average contact time in the settler or other means employed to separate the reactants and product from the effective, immiscible acid catalyst, and as used herein contact time shall have this meaning.

Where actual contact times of about a minute or more are indicated in accordance with the principles of our invention, the usual commercial reactors at present employed may be utilized by making an appropriate correction for the residence time in the reactor to take into account the additional contacting in the gravity settler, particularly Where contact times of less than five minutes are indicated in which case correction is particularly advisable.

Where contact times of less than one minute are indicated, particularly where contact times of but a few seconds are indicated, single pass reactors may be used as indicated above. With very short contact times special means or methods may be used to separate the reactants and catalyst, or to otherwise stop the reaction. Centrifugal separators may be employed to accelerate the phase separation. The catalyst may be killed by dilution to a concentration below its effective value as disclosed and claimed in U. S. Patent 2,392,962. Rapid chilling of the emulsion to lower its temperature and thus slow down the isomerization reactions may be suflicient in many cases.

The results which may be obtained by operating in accordance with the principles of our invention are illustrated in the following examples, wherein experimental results are tabulated for brevity and clarity comparing operations under the time-temperature-isomeric olefin distribution relationship found to exist by our invention with prior art operating conditions. Many of the examples of the invention were performed at low temperatures to obviate difiicuity in small scale laboratory batch discontinuous operations in obtaining very short contact times desired in many cases. Some of the continuous pilot plant runs performed at temperatures within the preferred operating range are included to confirm the relationships worked out more completely on a laboratory scale. Inthose cases where sufficient product was available for engine testing the octane ratings were determined. In other cases the product evaluation was made by careful analysis, particularly of the various components of the C8 fraction.

The experiments were performed in the liquid phase under substantially uniform conditions except as indicated, although in the very short residence time runs at normal temperature levels the relative amount of acid in the reaction emultime with the available equipment from about 40 to 60% used in the other experiments to over 20%. As pointed out in application Serial No. 561,883, now abandoned, referred to above, the increase in acid ratio per se effects improvement, but after discountin this factor the predicated degree of improvement in hydrocarbon distribution in product remains. The experimental results are tabulated below for each of the indision was necessarily increased to get the desired 10 vidual, substantially pure butene isomers.

Isobutene Example Number 1 Time in Minutes 7 Temperature, G Ratio lCl C4 Yield, Wt. Percent (Olefin Basis) Analysis, Wt. Percent:

Total Octane Rating of 180 0. end point aviation allzylate:

F3 clear +4.6 ce F-4 (S-icc.

Butene-Z Example Number 7 S 9 10 11 12 Time in Minutes 0 0. 2. 1 9 250 Temperature, O. i. 5 l5 15 -10 4() Ratio 1 15/ C4... 10 10. 3 3. 8 4. 2 Yield, Wt. perce 206 205 218 234 Analysis, Wt. percent:

Isu cn 2.11 l. 9 10. 7.0 18.00 Hcxan 1.03 1. 4 4. 3O 7. 00 Heptnnes U. 84 6. 8. Octanes- 2, 2, 4-1. M. P 24. 2, 9. 2, 3, 3-1. M. P 2,4-D.1\ 2, 3-D. Other 0 CH- Total 100. O0 100. G0 100. E0 100. 0 100. 00 100. 00 Octane Rating:

F-3 clear 94. G 95. 0 9G. 0 90. 4 89, 2

Butene-I Example Number l3 l4 15 1G l7 18 Time in Minutes 5 23 5 0. 10 9 250 Temperature, "C l0 0 9. 3 15 40 40 Ratio iC.1/=C4 4.05 4.05 4.05 10 4.2 4.2 Yield, Wt. percent (Olefin Basis) 182 216 189 190 191 202 Analysis, Wt. percent:

lsopentarlenfl 0.66 0.48 0.82 2.4 7 00 17. 20 Hexanes. 1.32 0.92 0.94 1.8 2 3.60 0. 99 0. [i3 1. 61 4 T0 6. 00

8.89 17.49 15 J 14.. 18 12.70 13. 10 11.67 18 8 13.1 ll. 30 6. 90

Octane Rating:

F-B clear F-4 s era T. 'E. mira e mam In order to illustrate the results to beobtained by the use of a mixture of the isomeric butenes, a butene mixture containing 23.6% butene-l, 18.8% isobutene, and 57.6% butane-2 (molar basis) was alkylated with hydrofluoric acid using a 9.0 to 1 isobutane-butene ratio, a reactor temperature of 60 F., a residence time of 2.1 minutes and to 1 acid to hydrocarbon ratio in a continuous system. The yield of debutanized alkylate was 204 weight percent on the basis of olefin consumed having an octane rating in the 180 C. end point aviation alkylate of 93.5 clear, 108.5 with 4.6 cc. of lead, and E4 rating of S+3.0 with 4.6 cc. of lead.

Comparing the results of Examples 1 to 4 with Examples 5 and 6, it will be seen that the percentage of trimethyl pentanes is very much higher in the former. On the other hand the percentage' of dimethyl hexanes is low in the first four examples, considerably higher in Example 5, and about half the total of the trimethyl pentanes in Example 6. This indicates that the trimethyl pentanes represent the primary or direct products of alkylation, and that as the alkylate hydrocarbon products remain in contact with the catalyst these desirable primary products isomerize towards an equilibrium mixture. Even ten minutes of contacting at 40 0., a residence time shorter than that usually employed .in present commercial practice produced a marked degradation in product quality. In order to achieve optimum product quality in the alkylation of isobutene very short contact times of the order of from a few seconds to not much above a minute are indicated 'for the usual commercial operating range of from to C. The marked efiect of temperature upon the contact time for optimum results is shown by a study of Examples 1, 2, 3 and 4, respectively, wherein the operating temperature was varied from 23.5 C. to +15 C. and the contact time reduced from minutes to 6 seconds with the resultant production of products of approximately the same high quality. The amount of 09+ hydrocarbons obtained in Examples 1, 2 and 3 is rather high due to the experimental procedure necessarily fol lowed in obtaining fairly short times in batch operation. The procedure employed gave rather high olefin concentrations which resulted in more polymerization and secondary alkylation than Would normally be obtained by continuous large scale operations under the same conditions as shown by Example 4. This condition of high polymerization is particularly noticeable in Example 3 wherein a time of 2 minutes was used in batch operation. For a predictionof continuous results at the lower temperatures, the distribution of products in the C5 to C8 fraction is more properly representative. A comparison of Example 5 with Example 6 shows the effect of the increasing importance of disproportionation reactions in increasing the amounts of C5 to C7 hydrocarbons and the (39+ hydrocarbons at the expense of the Cs hydrocarbon fraction. During this time, further isomerization of the Cs frac tion is also evident.

Similar results are also evident in the case of butene-2 as evidenced by a comparison of Examples 7, 8, 9 and 10 with Examples 11 and 12, One point of contrast in the case of butene-2 as compared with isobutene is that in the case of the former 2,3,4-trimethyl pentane as well. .as 2,2,4-trimethyl pentane represents a principal product, whereas in the case of isobutene 2,2,4- trimethyl pentane represents almost the sole C8 i0 hydrocarbon. By controlling the contact time carefully at the extreme lower limit, orby accepting some incomplete reaction and operating slightly below the lower limit of contact time, i. e.. an A value in Equation 3 defined hereinafter of about 21.5 substantially pure 2,2,4-trim'ethyl pentane may be obtained in continuous operation. in isobutene alkylation.

On the other hand in the case of butene-I, 2,3-dimethyl hexane represented the main pri-- mary product as shown by Examples 13, 14,15 and 16, and generally the amount of this hydrocarbon exceeded the total amount of trimethyl pentanes produced. With somewhat shorter contact times this hydrocarbon may be obtained in amounts constituting as high as '80 percent or more of the Ca hydrocarbon fraction, and by operating in accordance with our invention using the very short contact times this octane isomer may be obtained in a state of high purity in cases Where this material is desired for purposes other than a motor fuel blending agent. Further contacting of the butene-l alkylate with the catalyst results in product improvement since the isomerization occurs at the expense of the'dimethyl hexanes and results in the formation of trimethyl pentanes. As shown by a comparison of Example 17 with Example 18 the amount of this further contacting that may be tolerated without a net loss in the total amount of trimethyl pentanes and aviation aikylate product is limited by the simultaneous occurrence of disproportionation reactions.

Generally, by applying the principles of our invention, we have found that the butenes ina where =the actual contact time in minutes-ofreach ants and catalyst Tzthe temperature in degrees Kelvin me re q tbutesss fmol ;per cent butene-Z +mol per-cent isobutene E1, R, and C=constants, and B=a constant which is a function of the equi librium relationships between the-various Ce isomers, i. =e., approximately corresponds to the ratio of trimet-hyl pentanes to other octanes' at equilibrium under the operating condition of temperature and catalyst concentration chosen.

Over limited temperature ranges-values may be assigned to these constants C and B. These values have been experimentally determined and thus, based upon empirical determination over the operating range of from -10 C. to 70 0., itheequation correlating the dependent variables of time, temperature, and

isomeric olefin distribution: for optimum octane rating of the hydrofluoric acidbuteries alkylate' becomes where C has a value from 20.0 to 21:4, 'so'-"loiig as does not exceed a value given by Equation where C has a value from 18.7 to 19.5.

The first relationship is sound theoretically and indicates that as the isomeric olefin distribution approaches a value such that the primary alkylation products have a distribution corresponding to the equilibrium value for trimethyl pentanes with respect to the other Ca hydrocarbons, infinite contact time will not affect product quality. Expressed in terms of the equation as. the value of r approaches B, the term B-r approaches 5, and the log of 5 is infinity. Should r exceed B the expression gives a negative number and the equation is meaningless, but as a practicai matter, the isomerization reactions are actually efiecting product improvement at this point. At value of r greater than, equal to, or nearly as large as B, then Equation 2 governs the contact time since the equation determines the amount of contacting to effect product improvement that can be tolerated without achieving excessive disproportionation.

For each of the individual isomeric butenes the time required to obtain predominantly pure primary alkylation products (trime hyl penetanes in the case of butene-2 and isobutene, and 2,3 dimethyl hexane in the case of butene-l) is given by the expression where A has a value within the range of from 20.1 to 21.5 and and T have the meaning described in Equation 1.

The time-temperature relationship worked out in accordance with the principles of our invention are for liquid phase operation in which there is intimate contacting between the immiscible liquid catalyst and liquid hydrocarbons as an emulsified mixture. This emulsion mixture may be readily attained in the ordinary reactor provided with an agitator, or by turbulent flow through a pipe. The principles of our invention remain the same should other methods of contacting be employed since the effect would merely be to alter the reaction times of all the reactions involved at the particular reaction temperature chosen. Depending upon the particular butene isomer being alkylated, or the proportions of the various butene isomers in the mixture, the reaction may be terminated by applying the teachings of our invention either after the primary alkylat-ion reaction is completed or alter the desired amount of isomerization has occurred to procure the desired hydrocarbons or the maximum octane rating product in high yield.

The experimental results were also determined using acid of from 85 to 95 per cent titratable acidity in the reaction zone, and over this range the empirical values hold for the constants in the Equations 1, 2, and 3. This represents the range of titratable acidity usually employed and some variation therefrom may occur without appreciably affecting the time-temperature relationships. Obviously, however, the use of unusually low titratable acidities particularly where the acid contains as much as about percent or more of Water, would cut down the eificiency of the catalyst and result in the requirement of longer times for all of the desired and undesired reactions.

Generally the change of any reaction variable other than time, temperature, and butene isomer distribution from those at present employed in commercial alkylation and employed in the studies of our invention as set forth herein may be compared with present practice for its effect upon reaction rates by careful analysis of the product, and a suitable correction factor arrived at whereby the principles of our invention may be applied to obtain the desired products. A pure olefin isomer may be most readily used and the time at a given temperature required to complete alkylation determined (1. e., the time required for substantiall complete olefin disappearance) for the alkylation conditions to be employed. As a rough approximation the contact time for the alkylation reaction where isobutene or butene-Z represents the olefin to be alkylated, should be from one to twenty times and preferably from one to about ten times the time required to complete alkylation. The same relationship may be used for mixtures of isobutene and butene-2, and mixtures of these isomers with not more than an amount of butene- 1 equal to one-half the sum of the isobutene plus butene-2.

Having described our invention what we claim as new and desire to secure by Letters Patent is:

Process for the production of motor fuel of high octane rating from a butane-butene mixture containing isobutane, isobutene, butene-2 and butene-l in which the mol percent of butene-l is less than one-half the sum of the mol percent of butene-2 plus the mol percent of isobutene which comprises condensing the isobutane With the butenes in the liquid phase in a reaction zone in the presence of liquid hydrogen fluoride as the effective catalytic agent at a temperature of from l0 C. to 70 C., maintaining an external ratio of isobutane to total butenes feed to the reaction zone within the range of from 2 to 1 to 15 to 1, correlating the time of contact between catalyst and hydrocarbons with the average temperature of operation and the distribution of the isomeric butenes in the feed stock in accordance with the relationship where =the contact time in minutes, T=the temperature in degrees Kelvin,

mol per cent butene-l mol per cent butene-2+mol per cent isobutene and C has a value Within the range of 20.0 to 21.4.

JACK CALHOON DART. CARL S. KUHN, JR.

JOE E. PENICK. URBAN H. "WAGNER.

REFERENCES CITED '13; references are of record in the file of this patent:

UNITE?) STAIES PATENTS Certificate of Correction Patent No. 2,467,731. April 19, 1949.

JACK OALHOON DART ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 3, line 66, for the Word reaction, first occurrence, read reactions; column 4, line 26, for being read begin; column 5, line 48, for variable read variables; columns 7 and 8, second table, under the heading Butene-Z, first column thereof, next to the last line, for 4.6 cc. T. E. L. read +4.6 cc. T. E. L.; column 11, lines37 and 38, for the Words describe in read described above in; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 25th day of October, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

